This application claims the priority of Japanese Patent Document No. 2003-323029, filed Sep. 16, 2003, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a system and a method for controlling a motor vehicle and, more particularly, to a system and a method for controlling a motor vehicle mounted with a transmission that, when a gearshift is accomplished by selecting a dog clutch, transmits by way of a friction engagement device torque from a driving power source from an input shaft to an output shaft.
An automated manual transmission (hereinafter referred to as an “automated MT”) has been lately developed. The automated MT is a system automatizing operations of getting a vehicle started and gearshifts performed by a manual transmission that transmits torque of a driving power source from an input shaft to an output shaft through engagement of a gear and a dog clutch.
In a conventional vehicle mounted with an automated MT, a gearshift operation is performed by using an actuator that operates a friction clutch interposed between the driving power source and the input shaft of the transmission. As a result, the gearshift operation is disabled if the friction clutch is damaged. Then, in worst cases, the vehicle becomes unable to run.
Examples of known art are disclosed, for example, in Japanese Patent Laid-open No. Hei 8-230503 and PCT Patent Publication No. WO 95-22014 (an equivalent of Japanese Patent Laid-open No. 8-509284). In these known techniques, energy generated from a friction surface of the friction clutch is calculated and controlled to prevent the friction clutch from being damaged due to an increased temperature. In PCT Patent Publication No. WO95-22014, for example, an approach as detailed in the following is taken. Specifically, the overall energy that has already been generated is calculated based on an engine rotational speed, an input shaft rotational speed, and the transmission torque of the friction clutch. The natural cooling energy is then subtracted from the overall energy to arrive at the energy generated on the friction surface of the friction clutch. It is further known that the friction clutch is protected by minimizing the energy generated on the friction surface of the friction clutch in the following manner. Specifically, engagement of the friction clutch is rapidly released or a rapid engagement of the friction clutch is promoted according to the value of the calculated energy.
The automated MT has the disadvantage that there is an interruption of torque transmitted from the driving power source due to release and engagement operations of the friction clutch during gearshifts. This gives passengers of the vehicle a sense of discomfort. Known as a method of controlling gearshifts in the automated MT is an automatic transmission provided with a friction engagement device as disclosed in Japanese Patent Laid-open No. Sho 61-45163. In this method, when accomplishing a gearshift through selecting a dog clutch, the friction engagement device is controlled so as to transmit the driving power source torque to the output shaft of the transmission even during the gearshift. The method thereby avoids torque interruption, achieving a smooth shift feel.
The techniques disclosed in Japanese Patent Laid-open No. Hei 8-230503 and PCT Patent Publication No. WO95-22014 are effective in protecting the friction clutch, but are not directly applicable to the automatic transmission provided with the friction engagement device such as that disclosed in Japanese Patent Laid-open No. Sho 61-45163. To state it another way, the friction engagement device differs from the friction clutch used in PCT Patent Publication No. WO95-22014 in the purpose of use, method of use, frequency of use, and operating conditions. The friction engagement device without its modification is not thus directly applicable to the automatic transmission provided with the friction engagement device.
The automated MT using the friction engagement device as disclosed in Japanese Patent Laid-open No. Sho 61-45163 therefore has the problem that a broken friction engagement device aggravates a gearshift feel and, in worst cases, could make the automated MT totally disabled in gearshift.